Experimentally tested performance and emissions advantages of using natural-gas and hydrogen fuel mixture with diesel and rapeseed methyl ester as pilot fuels

Higher unburned hydrocarbon emissions are attributed to the relatively low temperature combustion of natural gas in compression ignition engines whereas the combustion of hydrogen in compression ignition environment results in higher NOX. These emissions characteristics are explained on the basis of different physio-chemical properties of the two gaseous fuel: higher Cp value in case of natural gas and higher diffusion coefficient, wider flammability limits and shorter quenching gaps for hydrogen are held responsible for these trends. This study assesses the potential of hydrogen being used in combination with natural gas with diesel and rapeseed methyl ester (RME) as pilot fuels. This type of fueling can be referred as 'triple fueling of the compression ignition engines' and has the potential to achieve a better trade-off between the higher NOX associated with hydrogen and higher hydrocarbon emissions associated with natural gas based dual fueling of compression ignition engines. The present study has investigated the potential of the triple fueling of the compression ignition engines so far the attainment of a better trade-off between NOX and hydrocarbon emissions are concerned. Comparing the specific NOX and hydrocarbon emissions in different cases reveals that a significant drop in specific hydrocarbon emissions can be achieved at the cost of a small increment in specific NOX. At both speeds (1000 rev/min and 1500 rev/min), the reduction in hydrocarbon emissions is more prominent at relatively lower loads, which can be a potential solution of reducing specific hydrocarbon emissions at lower loads in diesel engine operations. The stoichiometric equation for the triple fueling (Diesel or RME piloted mixture of natural gas and hydrogen) is also presented.